Nutrition and public policy expert Marion Nestle answers readers' questions in this monthly column written exclusively for The Chronicle. E-mail your questions to food@sfchronicle.com, with "Marion Nestle" in the subject line.

Q: What do you think of the new Dietary Guidelines that were announced earlier this week? Is there anything very new or different? And how important are these guidelines, anyway?

A: I was stunned by the first piece of the 2010 Dietary Guidelines for Americans that I saw online (dietaryguidelines.gov): "Enjoy your food, but eat less."

Incredible. The federal government finally recognizes that food is more than just a collection of nutrients? It finally has the nerve to say, "Eat less?"

But this statement and others directed to the public do not actually appear in the guidelines. That document repeats the same principles that have appeared in dietary guidelines for decades.

The 2010 guidelines just state them more clearly. (For the news story on the guidelines, go to sfg.ly/gdgsc0.)

But the "eat less" advice is about nutrients: sodium, saturated fat, cholesterol and trans fats. The guidelines even coin a new term for the "eat less" nutrients of greatest concern: "solid fats and added sugars," annoyingly abbreviated as SoFAS.

Official policy

Dietary guidelines are an official statement of federal nutrition policy. They influence everything the government says and does about food and nutrition. The guidelines determine the content of school meals, the aims of food assistance programs and the regulation of food labeling and advertising.

But their most powerful effect is on the food industry.

Why? Because advice to eat less is very bad for business.

Banal as their recommendations may appear, dietary guidelines are hugely controversial. That is why I was so surprised by "Enjoy your food, but eat less."

Consider the history. In 1977, a Senate committee chaired by George McGovern issued dietary goals for the United States. One goal was to reduce saturated fat to help prevent heart disease. To do that, the committee advised "reduce consumption of meat."

Those were fighting words. Outraged, the meat industry protested and got Congress to hold hearings. The result? McGovern's committee reworded the advice to "choose meats, poultry and fish which will reduce saturated fat intake."

This set a precedent. When the first dietary guidelines appeared in 1980, they used saturated fat as a euphemism for meat, and subsequent editions have continued to use nutrients as euphemisms for "eat less" foods.

Then came obesity. To prevent weight gain, people must eat less (sometimes much less), move more, or do both.

This puts federal agencies in a quandary. If they name specific foods in "eat less" categories, they risk industry wrath, and this is something no centrist-leaning government can afford.

Eat less, move more

So the new guidelines break no new ground, but how could they? The basic principles of diets that protect against chronic disease do not change. Stated as principles, the 2010 dietary guidelines look much the same as those produced in 1980 or by the McGovern committee.

Everything else in the guidelines tries to explain how to do this without infuriating food companies that might be affected by the advice. And the companies scrutinize every word.

The soy industry, for example, is ecstatic that the guidelines mention soy products and fortified soy beverages as substitutes for meat and as protein sources for vegetarians and vegans.

The meat industry is troubled by the suggestion to increase seafood, even though the guidelines suggest meal patterns that contain as much meat as always.

The salt recommendation - a teaspoon or less per day, and even less for people at risk for high blood pressure - is unchanged since 2005, but stated more explicitly. The salt industry reacted predictably: "Dietary guidelines on salt are drastic, simplistic and unrealistic."

In a few months, a new food guide will replace the old pyramid. Thanks to a law Congress passed in 1990, dietary guidelines must be revisited every five years. Expect the drama over them to continue.